Disable all the pretty stuff. Switch to the classic theme. Then go to control panel system and disable all visual effects (except for smooth fonts).

When gaming, consider using a game booster. I now recommend Wise Game Booster.

Other good tips for a fast machine.

If you are careful you don't need a real-time antivirus. Just get an on-demand free one, like ClamWinAV. An antivirus really slows down a system.

Consider switching your Windows to a Lite version of Windows. These are custom made, leaner versions of windows, that are around the web.

Update your BIOS or UEFI . Learn how to from the motherboard/laptop manufacturer and/or Google. This is dangerous, ask a friend if you can.

Disable all the devices (ex: IRQs) and any other stuff you don't need in the BIOS.

If you know for sure what type of hardware you have, tell the BIOS what it is, instead of letting the BIOS do the work (sometimes wrongly).

If you gonna try overclocking your machine make sure you have good ventilation. Overclocking sometimes is really worth it although a bit dangerous.

If your machine is slow one of the easiest ways to upgrade is to buy more memory for it, or sometimes a bigger hard disk or a SSD disk. Check if you need it and can. Buying a newer graphic card is also an option.

If all of these things don't help you even after formatting your machine, then you need a new computer. If you want help building a machine, mail me.